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GLOSSARY 



GENE - self-producing molecule transmitted by 

 the chromosome which determines the de- 

 velopment of the characters of the individ- 

 ual, some of which may be solely embryonic. 



GENETIC LIMITATION - each cell must react 

 exclusively in accordance with the standards 

 of the species which it represents. 



GENOME - haploid gene complex; minimum 



(haploid) number of chromosomes with their 

 genes derived from a gamete. 



GENOTYPE - the actual genetic make-up of an 

 individual, regardless of its appearance 

 (opposed to phenotype). 



GEOTONUS - position correct in respect to 

 gravity. 



GERM - the egg throughout its development, or 

 at any stage. 



GERM BAND - distinguishable bands of mate- 

 rial in the (Molluscan) egg which will give 

 rise respectively to ectoderm, endoderm, 

 and mesoderm of the embryo. 



GERM CELL - a cell capable of sharing in the 

 reproductive process, in contrast with the 

 somatic cell. (E. g. , spermatozoon or 

 ovum. ) Syn. gamete. 



GERM LAYER - a more-or-less artificial 

 spatial and histogenic distinction of cell 

 groups beginning in the gastrula stage, con- 

 sisting of ectoderm, endoderm and meso- 

 dermal layers. No permanent or clear cut 

 distinctions, as shown by train splantation 

 experiments. 



GERM RING - ring of cells which show accel- 

 erated mitotic activity, generally a synonym 

 for the marginal zone which becomes the 

 lips of the blastopore. The rapidly advanc- 

 ing cells in epiboly. (Syn. , marginal zone) 



GERM WALL - advancing boundary of the (chick) 

 blastoderm including syncitia and the zone 

 of junction. 



GERMINAL LOCALIZATION - every area of the 

 blastoderm (or of the unfertilized egg) cor- 

 responds to some future orgcin. Unequal 

 growth produces the differentiation of parts 

 (His, 1874). This concept led to the Mosaic 

 Theory of Roux. (See fate map. ) 



GERMINAL VESICLE - the pre -maturation 

 nucleus of the egg. 



GERONTOMORPHOSIS - phylogenetic effects 

 produced by modifying characters which 

 are present in the line of adults. 



GESTALTEN - a system of configurations con- 

 sisting of a ladder of levels; electron, atom, 

 molecule, cell, tissue, organ, and organ- 

 ism, each one of which exhibits specifically 

 new modes of action that cannot be under- 

 stood as mere additive phenomena of the 

 previous levels. With each higher level new 

 concepts become necessary. The parts of 

 a cell cannot exist independently, hence the 

 cell is more than a mere aggregation of its 

 parts, it is a patterned whole. Coherent unit 

 reaching a final configuration in space 

 (W. Kohler). Gestaltung nneans formation. 



GESTATION - period of carrying the young 

 (mammal) within the uterus. 



GIBBS-THOMPSON LAW - solidification from 



the accumulation of surface -acting substances 

 by the lower surface tension at the surface 

 of a drop (or cells), causing the potential 

 energy of the combined system (liquid drop 

 immersed within another liquid drop with 

 which it is not miscible) to drop to a min- 

 imum. 



GONOCHORISM - development or history of sex 

 differentiation (Haeckel). Opposed to her- 

 maphroditism. 



GONOMERY - continued separation during cleav- 

 age of the chromosome sets from sperm and 

 from egg in hybrid crosses. Theory that the 

 maternal and paternal chromosomes remain 

 apart throughout development. 



GRADIENT - gradual variation along an axis, 

 scaled regions of preference, two-dimen- 

 sional pattern, (gefalle of Boveri. ) (See 

 writings of Child. ) 



GRADIENT, ACTIVITY - gradient established 

 with appearance of the grey crescent in the 

 amphibian egg, extending dorso-ventrally 

 across the equator. 



GRADIENT, AXIAL - metabolic gradient deter- 

 mined by differences in electrical potential 

 or by experiments demonstrating differential 

 susceptibility (e. g. , to KCN). 



GRADIENT CONCEPT - idea of physiological 

 polarity indicated when an individual (<. g. , 

 Planaria) is transsected and each fragment 

 reproduces the missing portions while re- 

 taining the original polarity; any two-dimen- 

 sional concentration gradient as shown, for 

 instance, by animalizing or vegetalizing 

 factors in early morphogenesis (Ruiinstrom). 



GRADIENT, INHIBITION - refers to the balance 

 of animal and vegetal hemisphere gradients 

 in the (sea urchin) egg (Ruiinstrom) which 

 gradients are actually antagonistic to each 

 other and yet both are necessary for normal 

 (balanced) development. 



GRADIENT, PIGMENT - when pigment is pres- 

 ent it is generally concentrated at the cen- 

 ters of greatest metabolic activity. 



GRAFT - a portion of one embryo removed and 

 placed either among the tissues (a trans- 

 plant) or the membranes (e. g. , chorio- 

 allantoic graft) of another embryo. 



GRAFT, CHORIO-ALLANTOIC - method of 

 growing a graft on the extra-embryonic 

 membranes of the chick, the membranes 

 reacting to the local irritation of a (foreign) 

 graft in such a manner as to surround it 

 with a richly vascular tunic of indifferent 

 tissue, rich in the requisites for survival, 

 growth, and differentiation of the graft. 

 The graft is never incorporated as a trans- 

 plant by the host itself. Graft on the chick 

 chorio-allantois. 



GRAFT HYBRID - organism formed from host and 

 graft, showing characteristics of both stocks. 



